Installation for filling a mould with liquid metal and process employing this installation

ABSTRACT

The installation according to the invention comprises at least one mould, a vessel intended to receive the liquid metal and means for directly determining the evolution of the level of molten metal in the impression of the mould. These determination means comprise means for detecting the presence of this liquid metal in the impression, particularly of electromagnetic nature, which are adapted to penetrate at least partially in the interior volume of this impression.

FIELD OF THE INVENTION

The present invention relates to an installation for filling a mould with liquid metal, as well as to a process allowing this installation to be employed.

BACKGROUND OF THE INVENTION

In the technical domain of foundrywork, it is known to employ a succession of moulds, also called boxless moulds, which are made of sand. Each mould conventionally comprises a casting bowl intended to receive the molten metal, as well as at least one impression connected to this bowl via a feed channel. In service, it is question of displacing each mould in the direction of a casting machine adapted to pour molten metal.

This casting operation is subjected to several requirements.

Firstly, it is important to flood the casting bowl rapidly and to maintain it in the full state while the metal is propagating in the direction of the impressions. In effect, this ensures high-quality casting, bereft of voids, defects and trapped gas.

It is also necessary that the flowrate of metal swallowed by the mould be permanently equal to the flowrate delivered by the casting machine, in order to avoid any overflow, as well as any under-feed. Finally, at the end of casting, the level of metal in the bowl must be controlled in order that it fills the mould exactly, without, however, provoking any overflow.

It is firstly known to proceed with filling these moulds manually, namely this operation is carried out by an operator. It is also possible to carry out this filling automatically, so that it is piloted by programmable equipment.

For example, optical systems are known which employ a beam directed towards the casting bowl in order to determine the level of filling of the bowl during the casting. However, this known solution presents a drawback, connected in particular with its lack of knowledge of the real level of filling of the mould in the course of the casting process.

This being specified, the invention aims at proposing an installation for controlling the filling of a mould with liquid metal, reliably and precisely.

SUMMARY OF THE INVENTION

To that end, the invention relates to an installation for filling a mould with liquid metal, comprising:

-   -   at least one mould comprising a casting bowl, a feed channel, as         well as at least one impression connected to said bowl by said         channel,     -   a vessel intended to receive the liquid metal having to be cast         into the mould; and     -   means for directly determining the evolution of the level of         molten metal in the impression, these determination means         comprising means for detecting the presence of this liquid metal         in the impression, these detection means being adapted to         penetrate at least partially in the interior volume of this         impression.

According to other characteristics of the invention:

-   -   the detection means are of electromagnetic nature;     -   the determination means comprise means for creating an         electromagnetic field, of which lines of field form said         detection means, these lines of field being able to be disturbed         by the liquid metal present in the impression;     -   the means for creating the electromagnetic field comprise at         least one emitter coil, an electric generator adapted to excite         this emitter coil, as well as at least one receiver coil adapted         to cooperate with said emitter coil;     -   two receiver coils are provided, a first receiver coil being         placed between the emitter coil and the mould, while the other         receiver coil is placed opposite the emitter coil with respect         to the mould;     -   the determination means also comprise means adapted to transform         the intensity of the disturbance undergone by said lines of         field into an analog signal representative of the evolution of         the level of liquid metal in the impression, this analog signal         corresponding for example to the evolution of a voltage as a         function of the level of filling of the mould;     -   the determination means also comprise means for obtaining an         instantaneous curve, from said analog signal, representative of         the evolution of the level of molten metal in the impression, as         well as means for comparing this instantaneous curve with a         reference curve, while means are, in addition, provided for         controlling the flowrate of molten metal poured from the vessel,         in the event of the instantaneous curve differing from the         reference curve to an inadmissible extent;     -   the control means are adapted to actuate a mobile stopper with         which the vessel is equipped.

The invention also relates to a process for employing the installation as defined hereinabove, comprising the following steps of:

-   -   actuating the means for creating the electromagnetic field so as         to generate lines of field penetrating at least partially in the         interior volume of the impression; and     -   determining the evolution of the level of liquid metal in the         impression, as a function of the intensity of the disturbance         undergone by these lines of field.

According to other characteristics of the invention:

-   -   said instantaneous curve and said reference curve are compared         and the flowrate of liquid metal poured from the vessel is         modified if the difference between this instantaneous curve and         this reference curve is inadmissible;     -   the flowrate of liquid metal is modified by displacing said         stopper;     -   a predetermined threshold of the impression is chosen, the         instant is detected at which the level of liquid metal reaches         this threshold, a latent period is allowed to lapse, depending         in particular on the instantaneous value of the flowrate of         molten metal poured from the vessel, and the admission of liquid         metal in the mould is stopped at the end of this latent period.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention will be described hereinafter with reference to the accompanying drawings, given solely by way of non-limiting example and in which:

FIG. 1 is a general view illustrating an installation for filling a sand mould with liquid metal, according to the invention.

FIG. 2 is a view similar to FIG. 1, illustrating the installation of FIG. 1 during the phase of filling proper, and

FIG. 3 is a graph representing the evolution of the level of molten metal as a function of time, inside an impression with which a mould equipping the installation of FIGS. 1 and 2 is provided.

DESCRIPTION OF PREFERRED EMBODIMENT

Referring now to the drawings, the installation of FIGS. 1 and 2 comprises different moulds, of which only one has been shown, given reference 2. In service, this mould circulates beneath a vessel 4 which is filled with a liquid molten metal 6 which is for example cast-iron or steel. This metal was poured in the vessel 4 in conventional manner via a ladle (not shown).

The bottom of the vessel 4 is closed, in known manner, by a stopper 8, also called stopple. The latter may be manoeuvred along its principal axis, namely vertically in FIG. 1, via an actuator 9 of conventional type.

Each mould, which is of globally parallelepipedic shape, conventionally comprises a casting bowl 10, of truncated shape, into which flows the molten metal 6 poured from the vessel 4. This bowl 10 extends in a feed channel 12 which opens out into at least one impression 14. In the example described and shown, two such impressions 14 are provided, which have been illustrated schematically.

The installation of FIGS. 1 and 2 also comprises means for determining the evolution of the level of molten metal, inside the impression 14. It is firstly question of three electromagnetic coils, mounted on the same axis, horizontal in the present case.

More precisely, a central emitter coil 16 is provided, adapted to be excited by a sinusoidal electric signal whose frequency is some kilohertz. To that end, the coil 16 is placed in relation with an appropriate generator 18, of type known per se.

The emitter coil is associated with two lateral, so-called receiver coils, of which one, 20, is placed in the vicinity of the mould 2. On the other hand, the other receiver coil 22 is placed opposite this mould 2, with respect to the central emitter coil 16.

A single set of three coils has been shown in FIGS. 1 and 2, to the right of the mould. It should be noted that another set of coils may optionally be provided in the vicinity of the other impression, namely to the left in these Figures.

By way of additional variant, the coils may be placed above the mould, or in the vicinity of a corner thereof. In that case, the axis of these coils is respectively either vertical or oblique.

When the generator 18 feeds the emitter coil 16, an electromagnetic field is created, which circulates between the receiver coils 20 and 22. The lines of field thus created are illustrated in FIGS. 1 and 2 where they are represented by broken lines.

More precisely, 24 denotes the lines of field which circulate in the vicinity of the first receiver coil 20. As FIGS. 1 and 2 show, these lines 24 extend in part in a zone noted 24′, within the interior volume of the impression 14. On the other hand, the lines of field 26, extending in the vicinity of the other receiver coil 22, namely opposite the coil 20, do not interfere with the impression 14.

The three coils 16, 20 and 22 are, furthermore, connected, via a line 28, to an electronic unit 30 whose functions will be described hereinbelow. Finally, this unit 30 is connected, via a control line 32, with the actuator 9.

Functioning of the filling installation described hereinabove will now be explained in the following:

The actuator 9 must firstly be manoeuvred in order to open the stopper 8 so as to admit molten metal into the casting bowl 10. This molten metal then progressively fills the feed channel 12, then penetrates inside the impressions 14, as illustrated in FIG. 2.

It will be appreciated that, as it rises in the impression 14, the liquid metal is such as to disturb the electromagnetic field generated by the coils 16, 20 and 22, in particular in zone 24′ of the lines of field 24. Under these conditions, these lines of field, which penetrate in part in the interior volume of the impression, are adapted to detect the presence of the molten metal in this impression.

Furthermore, it is to be noted that the intensity of the aforementioned disturbance increases as the impression 14 is filled. Under these conditions, the electronic unit 30 is adapted to transform the value of the disturbance undergone by the lines of field 24 into an analog signal which corresponds for example to a variation of the voltage as a function of the real level of filling of the impression 14. The value of this voltage is consequently representative, at each instant, of the level of metal in the impression.

FIG. 3 is a graph illustrating this evolution of the voltage thus determined by the electronic unit 30, as a function of time. A zone noted I is firstly observed, in which this voltage is zero, this corresponding to the absence of interference of the molten metal with the lines of field 24. Then, from the instant when this interference begins to occur, the voltage increases with time, as the impression 14 is filled with the molten metal. This phase of rise of the level of this molten metal corresponds to zone II of this graph.

It should then be verified that the rise of the level of molten metal in the impression 14 occurs at an acceptable speed. To that end, a previous phase of apprenticeship is effected, allowing access to a curve (not shown) figuring the evolution of the voltage as a function of the real level of filling of the impression 14, during a so-called reference filling.

Then, if the electronic unit 30 ascertains that the instantaneous evolution of the voltage differs in inacceptable manner from this reference curve, this unit 30 controls the actuator 9, via the line 32. More precisely, if the instantaneous voltage is clearly greater than the reference voltage, at a given instant, the flowrate of molten metal poured from the vessel 4 must be reduced by lowering and even closing the stopper 8. On the other hand, if this instantaneous voltage is clearly lower than the reference voltage, the stopper 8 should be raised in order to increase the flowrate of molten metal administered from this vessel 4.

Furthermore, the final phase of the casting of molten metal is effected in the following manner. The instant at which the level of molten metal reaches a predetermined threshold of the impression, which is materialized by reference S visible in FIG. 2, should firstly be detected. It is appreciated that, at that instant, the voltage plotted on FIG. 3 attains a corresponding value, noted V_(s).

Then a latent period is allowed to lapse, which depends on the instantaneous value of the flowrate of molten metal poured from the vessel 4. Finally, at the end of this period, the electronic unit 30 controls the actuator 9 so as to provoke closure of the stopper 8, this stopping feed of molten metal.

It should be noted that the range and sensitivity of the sensor constituted by the three coils 16, 20 and 22, may be adapted as a function of the characteristics of the mould. For example, if each of these coils is formed by 200 turns, which present a rectangular section of 140 mm by 110 mm and are separated from one another by a distance of 210 mm, the corresponding range of measurement inside the mould presents a depth of 300 mm over a surface of about 200 mm by 250 mm, centred on the coils.

In addition, it will be noted that the arrangement of the three coils 16, 20 and 22 is advantageous, since the receiver coils 20 and 22 are mounted in opposition, namely the coil 20 is adjacent the mould, while the coil 22 is thereopposite. In this way, only the lines of field 24 are disturbed when the metal rises, while those, 26, do not undergo such a disturbance. Consequently, the electronic unit 30 benefits in manner known per se, from a regime of differential signals, thus allowing the sensitivity of the measurement to be increased.

The invention makes it possible to attain the objects set forth hereinabove.

In effect, the prior art employs an optical measurement in the casting bowl, which proves to be very poor in data since it is not representative of the level of molten metal in the impression. Such a measurement thus corresponds solely to the image of the difference between, on the one hand, the feed flowrate of the molten metal from the vessel 4 and, on the other hand, the instantaneous flowrate swallowed by the mould.

On the other hand, the invention takes advantage of a means for detecting the level of the molten metal which is adapted to penetrate in the impression itself. Consequently, the invention gives a direct character to the measurement thus effected, this guaranteeing a possibility of monitoring the level of filling, during a large part of the filling process. 

1. Installation for filling a mould with liquid metal, comprising: at least one mould comprising a casting bowl, a feed channel, as well as at least one impression connected to said bowl by said channel, a vessel intended to receive the liquid metal having to be cast into the mould; and means for directly determining the evolution of the level of molten metal in the impression, these determination means comprising means for detecting the presence of this liquid metal in the impression, these detection means being adapted to penetrate at least partially in the interior volume of this impression.
 2. The installation of claim 1, wherein the detection means are of electromagnetic nature.
 3. The installation of claim 2, wherein the determination means comprise means for creating an electromagnetic field, of which lines of field form said detection means, these lines of field being able to be disturbed by the liquid metal present in the impression.
 4. The installation of claim 3, wherein the means for creating the electromagnetic field comprise at least one emitter coil, an electric generator adapted to excite this emitter coil, as well as at least one receiver coil adapted to cooperate with said emitter coil.
 5. The installation of claim 4, wherein two receiver coils are provided, a first receiver coil being placed between the emitter coil and the mould, while the other receiver coil is placed opposite the emitter coil with respect to the mould.
 6. The installation of claim 3, wherein the determination means also comprise means adapted to transform the intensity of the disturbance undergone by said lines of field into an analog signal representative of the evolution of the level of liquid metal in the impression, this analog signal corresponding for example to the evolution of a voltage as a function of the level of filling of the mould.
 7. The installation of claim 6, wherein the determination means also comprise means for obtaining an instantaneous curve, from said analog signal, representative of the evolution of the level of molten metal in the impression, as well as means for comparing this instantaneous curve with a reference curve, while means are, in addition, provided for controlling the flowrate of molten metal poured from the vessel, in the event of the instantaneous curve differing from the reference curve to an inadmissible extent.
 8. The installation of claim 7, wherein the control means are adapted to actuate a mobile stopper with which the vessel is equipped.
 9. Process for employing the installation of claim 3, comprising the following steps of: actuating the means for creating the electromagnetic field so as to generate lines of field penetrating at least partially in the interior volume of the impression; and determining the evolution of the level of liquid metal in the impression, as a function of the intensity of the disturbance undergone by these lines of field.
 10. The process of claim 9, wherein said instantaneous curve and said reference curve are compared and the flowrate of liquid metal poured from the vessel is modified if the difference between this instantaneous curve and this reference curve is inadmissible.
 11. The process of claim 10, wherein the flowrate of liquid metal is modified by displacing said stopper.
 12. The process of claim 9, wherein a predetermined threshold of the impression is chosen, the instant is detected at which the level of liquid metal reaches this threshold, a latent period is allowed to lapse, depending in particular on the instantaneous value of the flowrate of molten metal poured from the vessel, and the admission of liquid metal in the mould is stopped at the end of this latent period. 